In the field of signal processing, computer processing and signal transmittion processing are carried out through conversion between analog format and digital format. In this field, extremely high speed signal converters, that is, very high speed analog to digital converters or very high speed digital to analog converters, are required in order to make the most of the performance of the computers and signal transmission systems. As typically in the neurocomputers, it has been proposed to use analog signal processing in computers. In this case, the conversion prcesses between analog signals and digital signals take the most part of the computer processing.
By use of the Josephson devices with high speed operation ability, several high performance systems can be constructed. Some analog to digital converters fulfilling the above requirement have been proposed, for instance, in C. A. Hamilton et. al., "Superconducting A/D Converter Using Latching Comparators", IEEE Trans. Magn., Vol. MAG-21, No. 2, pp. 197-199, Mar. 1985 and U.S. Pat. No. 4,956,642. On the other hand, any digital to analog converter fulfilling the above requirement has not been proposed. Such a digital to analog converter is important itself, and further a more complicated functional system such as an analog to digital converter can be constructed by use of the digital to analog converter. Therefore, digital to analog converters having simple construction, high precision and very high processing speed have very wide usability.